The objective of extraction is to expel or squeeze the juice from a sample of sugarcane, representative of a load for delivery to a sugar mill and/or refinery in order to determine, before purchase, the sugar content of the load of sugarcane. The so-called press method has the advantage of providing high speed analysis and exceptional accuracy in the reproducibility of its analyzing cycles.
The pressure exerted on a sample of sugarcane placed in a perforate filter cup, also known as the bucket, is maintained at a strictly constant maximum value for a predetermined period, so as to ensure the extraction of nearly all the juice contained in the sugarcane.
The juice is analyzed physically to determine the saccharine content. The remaining "cake" of bagasse or megass is weighed. The weight of the bagasse and the amount of sugar are the two parameters taken into consideration for calculating the price paid to the grower for his sugarcane.
The extraction technique, the configuration and arrangement of the perforate filter cup, the shape of the perforations, etc., are designed so that not only as much as possible of the juice is extracted but also to prevent "reimbibition" or reabsorption of the juice back into the cake once the pressure exerted is released.
Present-day sample extractor presses are of simple design with two symmetrical handling stations and a vertically displaceable piston. The juice receptacle on which the removable perforate cylindrical filter cup is centered is attached to a movable carriage which has two end of course positions, a pressing position and a retracted position for loading surgarcane sample and ejecting the compressed depleated cake.
The cake, though, is held in the bottom of the filter cup. It is therefore necessary to dislodge it to cause it to drop to a drawer provided on each work table.
As a trade-off to the low cost and easy operation of the extractor press are its various drawbacks, inter alia, the handling of filter cup which is a tiresome operation for the operator; the impossibility of loading the filter cup when it is not in the receptacle; the ejecting of the cake by hand; and the low operating speed or hourly output.
The full operating cycle takes three and a half minutes of which the pressing of the sample lasts a total of two minutes which limits the hourly rate to a maximum of 17 analyses per hour.